Distribution Of EDNA In Activated Sludge And Fouling Layer In MBR And Its Effect On Membrane Fouling

Compared with conventional activated sludge?CAS?,membrane bioreactor?MBR?has many distinct advantages,which applied extensively in wastewater treatment.However,membrane fouling is still the major obstacle for the further development of MBR.Among fouling processes,biofouling can highly reduce permeability of membrane,and microorganisms can easily attach onto membrane surface followed by secretion of extracellular polymeric substances?EPS?,which accelerates the formation of biofilm.Recent studies have reported that eDNA?extracellular DNA?function as a scaffold determining three dimensional architecture and permeability of biofilm.Therefore,a comprehensive investigation on the role of eDNA on biofilm formation is vital for revealing membrane.Based on a continuously operated MBR,this paper focused on the distribution of eDNA in MBR.Firstly,the dynamic distribution of eDNA in sludge mixed liquor was monitored during the entire operation time,and the action mechanism of eDNA on bioflocculation was analyzed.The dynamic distribution of eDNA in fouling layer on membrane surface under different transmembrane pressure?TMP?was investigated,and the action mechanism of eDNA on adherence of fouling alyer was revealed.Combining with batch experiment,the relationship between eDNA and initial biofouling under different permeate fluxes conditions was investigated.The mian results are presented as follows:?1?The distribution characteristics of eDNA in EPS followed the sequence:TB-EPS?tight EPS?>LB-EPS?loose EPS?>S-EPS?soluble EPS?.The concentrations of eDNA in different fractions of EPS increased first and then decreased with operation time.There is a strong correlation between eDNA and PN in the inner layer of EPS?TB-EPS and LB-EPS??r=0.667,P<0.05;r=0.682,P<0.05?.The close correlation between eDNA and flocculation capacity of sludge floc was found in the inner layer of EPS?r=-0.777,P<0.05;r=-0.771,P<0.05?,the increase of eDNA content had a benefit to bioflocculation and enhanced the filterability of sludge mixed liquor.?2?The eDNA was mainly distributed in TB-EPS in fouling layer,and the concentration and proportion of eDNA in EPS in fouling layer increased first and then decreased.The eDNA content in initial fouling layer increase gradually,when TMP was less than 3.5 kPa.During formation of the initial fouling layer,the energy barrier between the fouling layer and membrane had an obvious decrease with the increase of eDNA content,which resulted in a serious membrane fouling potential.?3?The biofilm developed during 24 h under different permeate fluexs?0,5 and 10L?m²·h??conditions was analyzed through batch experiment.The results showed that tyrosine-like proteins were major substances.The level of eDNA was positively correlated with PN,aromatic-like proteins and tryptophan-like proteins in the initial biofilm?r=0.775,P<0.05;r=0.743,P<0.05;r=0.898,P<0.05?.There was a significant negative correlation between eDNA and?G ^AB_adh?r=-0.826,P<0.05?,and the present of eDNA strengthened attractive acid-base interactions between biofilm and membrane,which aggregated bioflouling.Furthermore,aromatic-like proteins and tryptophan-like proteins were significantly negative related to?G ^AB_adh?r=-0.885,P<0.05;r=-0.822,P<0.05?,suggesting that by binding with eDNA,proteins on the membrane surface enhanced attractive acid-base interactions responsible for biofilm formation.